Screening Of Dominant Strains For Activated Sludge Aerobic Digestion And Its Effect On Sludge Stabilization

With the activated sludge being widely used in various sewage treatment plants,its by-products(such as excess sludge)are increasingly produced.The excess sludge consists of organic matter,heavy metals,salts,pathogenic microorganism,parasite eggs and other poisonous and harmful substances.Therefore,the excess sludge without appropriate stabilizing treatment will cause secondary pollution to the environment.The popular sludge stabilization technologies in sewage treatment plants are aerobic digestion and anaerobic digestion.Aerobic digestion is widely used in small and medium-sized sewage treatment plants due to the convenient in management,low capital cost and stable treatment effect.However,the operation cost is relatively high since the digestion process need long time aeration.In this study,the dominant microbial strains were isolated from the excess sludge of long-term aerobic digestion to strengthen the sludge aerobic digestion,reduce sludge stabilization time,and thus reducing running cost.Three dominant strains which had obviously effects for sludge aerobic digestion have been isolated and domesticated.The 16 S r RNA gene sequencing results showed that the three strains belonged to Bacillus sp.,Pseudomonas sp.and Bacillus sp..During the aerobic digestion process,the degradation rate of MLSS and TOC was fast in the first 21 days and then entered a plateau.In the region of the fast rate,the sludge could be quickly reduced through the aeration,while the influence of aeration would become smaller in the plateau.Besides,the p H declined with the increase of aeration time in the short-term aerobic digestion process.Since the strains R3,R16 and R19 were vaccinated,the sludge have achieved stabilization at the ninth day,tenth day and ninth day,respectively,with a TOC removal rate over 40%.Compared with the control group,the sludge stabilization occurred 4 days,3 days and 4days earlier and the SVI value were 14.1%,9.0% and 11.1% lower.Besides,the MLSS degradation rate were 7.1%,3.3% and 8.2% higher at the thirteenth day.In addition,the dominant strains would result TOC,nitrate nitrogen and amino nitrogen acceleration and phosphorus release.At the thirteenth day of adding R19,the TOC degradation rate improved 7.29% and MLSS removal rate enhanced 7.8% in the reactor with the DO of 3-5 mg/L than in the reactor with the DO of 1-3 mg/L.The TOC degradation rate improved 0.97% and MLSS removal rate enhanced 2.01% in the reactor with the DO of 5-6 mg/L than in the reactor with the DO of 3-5 mg/L.The TOC degradation rate improved 1.88% and MLSS removal rate enhanced 3.24% in the reactor with the DO of 6-7 mg/L than in the reactor with the DO of 3-5 mg/L.The TOC degradation rate and MLSS removal rate improved to different extents with the increase of DO in the reactor.Digestion efficiency was improved most during the DO increased to 3-5 mg/L,while the improvement responded unobviously to the continue increase in DO.The TOC degradation rate improved 7.67% and MLSS removal rate enhanced 7.58% in the reactor with the p H=6.5 than in acid environment when the R19 was added and DO remained 3-5 mg/L.Suitable p H was conducive to microbial enhanced sludge stabilization.At the thirteenth day of adding R19,the TOC degradation rate improved 45.34%,55.63%,58.20% and 59.13%,respectively and the MLSS removal rate enhanced 33.90%,42.32%,46.38% and 49.81%,respectively in the reactor with different addition ratio(0.5%,1%,2% and 5%).Increase in the dominant strains dosage can improve the treatment efficiency.However,the improvement of the treatment efficiency became less with the increase in the dominant strains dosage.Combination of different types of dominant strains can achieve different reinforcing effect,composition the R3,R16 and R19 three dominant strains respectively,reaction to the first 13 days,adding R3 and R19 combined reactor MLSS and TOC degradation rate were the highest,is 59%,49.21% respectively.Compared with R19 which's rate were 57.81% and 46.21%,respectively 1.19% and 3%,other combinations were lower than R19.